kernel/trace/ring_buffer.c

Source file repositories/reference/linux-study-clean/kernel/trace/ring_buffer.c

File Facts

System
Linux kernel
Corpus path
kernel/trace/ring_buffer.c
Extension
.c
Size
228411 bytes
Lines
8314
Domain
Core OS
Bucket
Scheduler, Processes, Timers, Sync, And Syscalls
Inferred role
Core OS: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

struct ring_buffer_meta {
	int		magic;
	int		struct_sizes;
	unsigned long	total_size;
	unsigned long	buffers_offset;
};

struct ring_buffer_cpu_meta {
	unsigned long	first_buffer;
	unsigned long	head_buffer;
	unsigned long	commit_buffer;
	__u32		subbuf_size;
	__u32		nr_subbufs;
#ifdef CONFIG_RING_BUFFER_PERSISTENT_INJECT
	__u32		nr_invalid;
	__u32		entry_bytes;
#endif
	int		buffers[];
};

/*
 * The ring buffer header is special. We must manually up keep it.
 */
int ring_buffer_print_entry_header(struct trace_seq *s)
{
	trace_seq_puts(s, "# compressed entry header\n");
	trace_seq_puts(s, "\ttype_len    :    5 bits\n");
	trace_seq_puts(s, "\ttime_delta  :   27 bits\n");
	trace_seq_puts(s, "\tarray       :   32 bits\n");
	trace_seq_putc(s, '\n');
	trace_seq_printf(s, "\tpadding     : type == %d\n",
			 RINGBUF_TYPE_PADDING);
	trace_seq_printf(s, "\ttime_extend : type == %d\n",
			 RINGBUF_TYPE_TIME_EXTEND);
	trace_seq_printf(s, "\ttime_stamp : type == %d\n",
			 RINGBUF_TYPE_TIME_STAMP);
	trace_seq_printf(s, "\tdata max type_len  == %d\n",
			 RINGBUF_TYPE_DATA_TYPE_LEN_MAX);

	return !trace_seq_has_overflowed(s);
}

/*
 * The ring buffer is made up of a list of pages. A separate list of pages is
 * allocated for each CPU. A writer may only write to a buffer that is
 * associated with the CPU it is currently executing on.  A reader may read
 * from any per cpu buffer.
 *
 * The reader is special. For each per cpu buffer, the reader has its own
 * reader page. When a reader has read the entire reader page, this reader
 * page is swapped with another page in the ring buffer.
 *
 * Now, as long as the writer is off the reader page, the reader can do what
 * ever it wants with that page. The writer will never write to that page
 * again (as long as it is out of the ring buffer).
 *
 * Here's some silly ASCII art.
 *
 *   +------+
 *   |reader|          RING BUFFER
 *   |page  |
 *   +------+        +---+   +---+   +---+
 *                   |   |-->|   |-->|   |
 *                   +---+   +---+   +---+
 *                     ^               |
 *                     |               |
 *                     +---------------+
 *
 *
 *   +------+
 *   |reader|          RING BUFFER
 *   |page  |------------------v
 *   +------+        +---+   +---+   +---+
 *                   |   |-->|   |-->|   |
 *                   +---+   +---+   +---+
 *                     ^               |
 *                     |               |
 *                     +---------------+
 *
 *
 *   +------+
 *   |reader|          RING BUFFER
 *   |page  |------------------v
 *   +------+        +---+   +---+   +---+
 *      ^            |   |-->|   |-->|   |
 *      |            +---+   +---+   +---+
 *      |                              |
 *      |                              |
 *      +------------------------------+
 *

Annotation

Implementation Notes